Mayor Michael Bloomberg isn't convinced that it would be worthwhile to spend billions of dollars on tidal barriers in an attempt to mitigate the impact of future superstorms on New York City's lower-lying neighborhoods.

"I don't know that I think there's any practical ways to build barriers in the oceans, when you have an enormous harbor like we do and Long Island Sound," said Bloomberg today. "Even if you spent a fortune, it's not clear to me that you would get much value from it. What we have to do is learn, and it would be great if you didn't put your generators in the basement."

The mayor is emphasizing less expensive solutions like stocking up on more well-positioned generators.

The wonkiest member of New York's congressional delegation has a different cost-benefit analysis of a prospective, massive tidal-barrier project.

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In August, Congressman Jerry Nadler sent a letter to the Mayor's Office of Long Term Planning about "the need to begin developing plans to protect the City’s waterfront infrastructure."

Nadler urged the city to "undertake a comprehensive study of various mechanisms, such as new bulkheads, sea walls and storm surge barriers, which could prevent damage to New York City’s waterfront infrastructure in the face of future threats from rising sea levels."

On Thursday, Nadler spent much of the day exploring the damage wrought by Sandy on a city left vulnerable by a lack of the very protections he described.

He visited the Brooklyn Battery Tunnel, just one half of which was still flooded with 43 million gallons of water. He visited Sea Gate, at the southwestern tip of Brooklyn, where, during the storm, Gravesend Bay met the Atlantic Ocean, destroying some 15 houses and leaving 10 feet of water in the basements of others.

He drove down Mermaid Avenue in Coney Island, which his aide described to me as "totally decimated."

"We have to take a serious look at the tidal barriers," said Nadler, speaking by cellphone from Sea Gate. "It's evident that with global warming, climate change, whatever you want to call it, these 100-year events are going to be a lot more often and a lot more violent, and we have to start planning for it."

He acknowledged that such technology is "very expensive."

"On the other hand, what's the cost of not being prepared?" he said. "How much is this going to cost us?"

In other words, if the city, state and country are going to pay one way or another, they might as well pay for preventative measures, not remedial ones.

And what of the argument that even with tidal barriers at the Verrazano, Throgs Neck and Arthur Kill, as some have proposed, many parts of New York City and Long Island would remain vulnerable, including the very Sea Gate he was visiting?

"I'm not sure how you could protect those areas, or if you could," he said. "But the fact that something doesn't solve 100 percent of your problems is not an argument against doing it, if it solves 70 percent of your problems."

Nadler suggested that other infrastructural fortifications were worth exploring, too.

"You look at lower Manhattan, maybe we should have retractable flood walls that go up 15 or 16 feet," he said.

I asked whether there was money available for that sort of thing.

"Of course there's money available," he said.

After all, whenever there's catastrophe, as there was this week, "somehow the money's found."

And what if the federal government doesn't come through? Would the state and city pay for such projects?

"Obviously what they don't do, we'll have to do if it's necessary to protect ourselves, no question," he said.

Nadler, who has long been a voice for increased infrastructure investment in New York City, may have more company now.

On Tuesday, once Sandy's devastation had become apparent, Governor Andrew Cuomo said, "We have to start to think about how do we redesign the system so this doesn't happen again."

"There is no weather pattern that can shock me at this point," he continued. "And I think that has to be our attitude. And how do we redesign our system and our infrastructure assuming that?"

On Thursday afternoon, the Regional Plan Association, the nation's oldest urban research organization, and the original proponent of a Second Avenue Subway and an X line, called for "a new approach to managing the impact of storms in the tri-state region."

One of several strategies the RPA suggested exploring is tidal barriers, of the sort used in London and Rotterdam.

The RPA also said the city and state should consider restoring barrier dunes and wetlands, elevating homes, buying out particularly vulnerable properties, reexamining land-use policies, creating more redundancy within the transit system and electrical systems, and sealing off transit stations, roads, tunnels, and utilities plants from water.

"Although the sums might seem daunting, the cost of preventative measures is far smaller than the toll suffered by the region when core infrastructure is battered and unusable, homes are damaged and destroyed, millions of residents are unable to get to work or school, and lives are lost," the RPA said.